CN111434131B - Method for managing UE context and apparatus supporting the same - Google Patents

Method for managing UE context and apparatus supporting the same Download PDF

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Publication number
CN111434131B
CN111434131B CN201880077818.XA CN201880077818A CN111434131B CN 111434131 B CN111434131 B CN 111434131B CN 201880077818 A CN201880077818 A CN 201880077818A CN 111434131 B CN111434131 B CN 111434131B
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rrc
context
message
gnb
base station
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CN111434131A (en
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金鉐中
卞普敬
徐健
边大旭
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LG Electronics Inc
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LG Electronics Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W48/00—Access restriction; Network selection; Access point selection
    • H04W48/20—Selecting an access point
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
    • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
    • H04L1/1607—Details of the supervisory signal
    • H04L1/1664—Details of the supervisory signal the supervisory signal being transmitted together with payload signals; piggybacking
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W68/00—User notification, e.g. alerting and paging, for incoming communication, change of service or the like
    • H04W68/005—Transmission of information for alerting of incoming communication
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/0005—Control or signalling for completing the hand-off
    • H04W36/0011—Control or signalling for completing the hand-off for data sessions of end-to-end connection
    • H04W36/0033—Control or signalling for completing the hand-off for data sessions of end-to-end connection with transfer of context information
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/08—Reselecting an access point
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W60/00—Affiliation to network, e.g. registration; Terminating affiliation with the network, e.g. de-registration
    • H04W60/04—Affiliation to network, e.g. registration; Terminating affiliation with the network, e.g. de-registration using triggered events
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W60/00—Affiliation to network, e.g. registration; Terminating affiliation with the network, e.g. de-registration
    • H04W60/06—De-registration or detaching
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W76/00—Connection management
    • H04W76/20—Manipulation of established connections
    • H04W76/27—Transitions between radio resource control [RRC] states

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Computer Security & Cryptography (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

A method of managing a UE context and an apparatus supporting the same are provided. According to one embodiment of the present invention, a method of managing a UE context in a wireless communication system includes the steps of: receiving a UE context request message including a Radio Resource Control (RRC) establishment cause from a second BS, wherein the first BS and the second BS are located in a same Radio Access Network (RAN) -based notification area (RNA); and transmitting a UE context response message to the second BS when the RRC establishment cause is related to the RNA update, wherein the UE context response message piggybacks an RRC message for requesting the UE to move to an RRC inactive state.

Description

Method for managing UE context and apparatus supporting the same
Technical Field
The present invention relates to a wireless communication system, and more particularly, to a method of managing a UE context performed by a first base station and a second base station and an apparatus supporting the same.
Background
In order to meet the increasing demand for radio data services after commercialization of the 4 th generation (4G) communication system, efforts have been made to develop an improved 5 th generation (5G) communication system or pre-5G communication system. Standardization for 5G mobile communication standard work has been formally started in 3GPP and is being discussed in the tentative name of new radio access (NR) in the standardization work group.
In addition, the upper layer protocol defines a protocol state to consistently manage an operation state of a User Equipment (UE) and to instruct functions and procedures of the UE in detail. In the discussion on NR standardization, RRC states are discussed such that rrc_connected states and rrc_idle states are basically defined and rrc_inactive states are additionally introduced.
Furthermore, there will be a problem when the UE informs the network using periodic RAN-based notification area updates (RNAUs) that it is still reachable in the RAN-based notification area. The UE transitions from the RRC-INACTIVE state to the RRC-CONNECTED state to perform RNAU. The new gNB should acquire the UE context from the anchor gNB every time the UE enters the RRC-CONNECTED state. However, after periodic RNAU, the UE returns to RRC-INACTIVE state and moves within the configured RAN-based notification area. This means that the UE context transfer is repeated each time an RNAU is triggered.
Disclosure of Invention
Technical problem
According to the prior art, a UE context should be acquired from a previous serving gNB to a new gNB whenever the UE accesses the gNB to inform the network that it is still reachable in the RAN-based notification area. Even when data transmission between UE and gNB does not occur during RNAU, it may cause unnecessary signaling and additional delay.
Technical scheme of the problem
According to an embodiment of the present invention, there is provided a method performed by a first Base Station (BS) in a wireless communication system. The method may comprise the steps of: receiving a UE context request message including a Radio Resource Control (RRC) establishment cause from a second BS, wherein the first BS and the second BS are located in a same Radio Access Network (RAN) -based notification area (RNA); and transmitting a UE context response message to the second BS when the RRC establishment cause is related to the RNA update, wherein the UE context response message piggybacks an RRC message for requesting the UE to move to an RRC inactive state.
The step of transmitting the UE context response message may include the steps of: determining that the first BS maintains the UE context based on RRC establishment cause related to RNA update; and generating a UE context response message that does not include the UE context requested by the UE context request message.
The first BS may be a previous serving base station and the second BS may be a current serving base station.
The RRC message may be an RRC resume message or an RRC release message.
The UE context response message may be a retrieve UE context failure message.
According to another embodiment of the present invention, there is provided a first Base Station (BS) in a wireless communication system. The first BS may include: a transceiver for transmitting or receiving radio signals; and a processor coupled to the transceiver, the processor configured to: the control transceiver receiving a UE context request message including a Radio Resource Control (RRC) establishment cause from a second base station, wherein the first base station and the second base station are located in a same Radio Access Network (RAN) -based notification area (RNA); and when the RRC establishment cause relates to the RNA update, controlling the transceiver to send a UE context response message to the second base station, wherein the UE context response message piggybacks an RRC message for requesting the UE to move to an RRC inactive state.
The processor may be further configured to: determining that the first BS maintains the UE context based on RRC establishment cause related to RNA update; and generates a UE context response message that does not include the UE context.
The first BS may be a previous serving base station and the second BS may be a current serving base station.
The RRC message may be an RRC resume message or an RRC release message.
The UE context response message may be a retrieve UE context failure message.
According to another embodiment of the present invention, there is provided a method performed by a second Base Station (BS) in a wireless communication system. The method may comprise the steps of: receiving, from a User Equipment (UE), a Radio Resource Control (RRC) recovery request message including an RRC establishment cause, wherein the RRC establishment cause relates to a Radio Access Network (RAN) -based notification area (RNA) update; transmitting a UE context request message including an RRC establishment cause to a first BS, wherein the first BS and a second BS are located in the same RNA; receiving a UE context response message from the first BS, wherein the UE context response message piggybacks an RRC message for requesting the UE to move to an RRC inactive state; and forwarding the RRC message to the UE.
The UE context response message may not include the UE context requested by the UE context request message.
The first BS may be a previous serving base station and the second BS may be a current serving base station.
The UE context response message may be a retrieve UE context failure message.
Advantageous effects of the invention
According to embodiments of the present invention, if the UE transmits a periodic RNAU and does not need to move the UE's context to the serving gNB, the previous serving gNB does not need to transmit the UE context to the current serving gNB, and the current serving gNB does not need to perform the core network and path switching procedure. That is, the anchor gNB may selectively acquire UE context toward the new gNB in order to reassign the role of the anchor gNB. For periodic RNAU, the anchor gNB may decide whether to transmit the UE context to the new gNB as the UE moves back to the RRC-INACTIVE state.
Drawings
Fig. 1 shows an example of a wireless communication system to which the technical features of the present invention can be applied.
Fig. 2 shows another example of a wireless communication system to which the technical features of the present invention can be applied.
Fig. 3 shows a block diagram of a user plane protocol stack to which the technical features of the present invention may be applied.
Fig. 4 shows a block diagram of a control plane protocol stack to which the technical features of the present invention may be applied.
Fig. 5 illustrates an RRC connection recovery procedure.
Fig. 6 illustrates an example of a method of managing a UE context according to an embodiment.
Fig. 7 illustrates another example of a method of managing UE context according to an embodiment.
Fig. 8 illustrates an example of a method of managing UE context according to the present invention.
Fig. 9 shows a structure of a network according to an embodiment of the present invention.
Fig. 10 illustrates an example of a method of managing UE context according to the present invention.
Fig. 11 shows a structure of a network according to an embodiment of the present invention.
Fig. 12 illustrates an example of a method of managing UE context according to the present invention.
Fig. 13 illustrates a structure of a UE according to an embodiment of the present invention.
Detailed Description
The technical features described below may be used by a communication standard of the 3 rd generation partnership project (3 GPP) standardization organization, a communication standard of the Institute of Electrical and Electronics Engineers (IEEE), and the like. For example, the communication standards of the 3GPP standardization organization include Long Term Evolution (LTE) and/or evolution of the LTE system. The evolution of the LTE system includes LTE-advanced (LTE-A), LTE-A Pro and/or 5G New Radio (NR). Communication standards of the IEEE standardization organization include Wireless Local Area Network (WLAN) systems such as IEEE 802.11 a/b/g/n/ac/ax. The above-described systems use various multiple access techniques, such as Orthogonal Frequency Division Multiple Access (OFDMA) and/or single carrier frequency division multiple access (SC-FDMA), for the Downlink (DL) and/or uplink (DL). For example, only OFDMA is available for DL and only SC-FDMA is available for UL. Alternatively, OFDMA and SC-FDMA may be used for DL and/or UL.
Fig. 1 shows an example of a wireless communication system to which the technical features of the present invention can be applied. Specifically, fig. 1 illustrates a system architecture based on an evolved-UMTS terrestrial radio access network (E-UTRAN). The above-described LTE is part of an evolved-UTMS (E-UMTS) using E-UTRAN.
Referring to FIG. 1, a wireless communication system includes one or more user equipments (UEs; 10), an E-UTRAN, and an Evolved Packet Core (EPC). The UE 10 refers to a communication device carried by a user. The UE 10 may be stationary or mobile. The UE 10 may be referred to by another term such as a Mobile Station (MS), a User Terminal (UT), a Subscriber Station (SS), a wireless device, etc.
The E-UTRAN consists of one or more Base Stations (BS) 20. The BS 20 provides the E-UTRA user plane and control plane protocol ends towards the UE 10. BS 20 is typically a fixed station that communicates with UE 10. The BS 20 hosts functions such as inter-cell radio resource management (MME), radio Bearer (RB) control, connection mobility control, radio admission control, measurement configuration/provisioning, dynamic resource allocation (scheduler), etc. A BS may be referred to as another term, such as an evolved NodeB (eNB), a Base Transceiver System (BTS), an Access Point (AP), etc.
The Downlink (DL) represents communication from the BS 20 to the UE 10. The Uplink (UL) represents communication from the UE 10 to the BS 20. The Side Link (SL) represents communication between UEs 10. In DL, a transmitter may be part of the BS 20 and a receiver may be part of the UE 10. In the UL, the transmitter may be part of the UE 10 and the receiver may be part of the BS 20. In SL, the transmitter and receiver may be part of the UE 10.
The EPC includes a Mobility Management Entity (MME), a serving gateway (S-GW), and a Packet Data Network (PDN) gateway (P-GW). The MME hosts functions such as Non Access Stratum (NAS) security, idle state mobility handling, evolved Packet System (EPS) bearer control, and the like. The S-GW hosts functions such as mobility anchoring. The S-GW is a gateway with E-UTRAN as an endpoint. For convenience, the MME/S-GW 30 will be referred to herein simply as a "gateway," but it will be understood that this entity includes both the MME and the S-GW. The P-GW hosts functions such as UE Internet Protocol (IP) address assignment, packet filtering, etc. The P-GW is a gateway with PDN as an endpoint. The P-GW is connected to an external network.
The UE 10 is connected to the BS 20 through a Uu interface. The UEs 10 are interconnected to each other through a PC5 interface. The BSs 20 are interconnected to each other by an X2 interface. BS 20 is also connected to the EPC through an S1 interface, more specifically to the MME through an S1-MME interface and to the S-GW through an S1-U interface. The S1 interface supports a many-to-many relationship between MME/S-GW and BS.
Fig. 2 shows another example of a wireless communication system to which the technical features of the present invention can be applied. Specifically, fig. 2 shows a system architecture based on a 5G new radio access technology (NR) system. An entity used in a 5G NR system (hereinafter, simply referred to as "NR") may absorb some or all of the functions of an entity (e.g., eNB, MME, S-GW) introduced in fig. 1. The entity used in the NR system can be identified by the name "NG" to distinguish from LTE/LTE-a.
Referring to fig. 2, the wireless communication system includes one or more UEs 11, a next generation RAN (NG-RAN), and a 5 th generation core network (5 GC). The NG-RAN is comprised of at least one NG-RAN node. The NG-RAN node is an entity corresponding to the BS 10 shown in fig. 1. The NG-RAN node is composed of at least one gNB 21 and/or at least one NG-eNB 22. The gNB 21 provides NR user plane and control plane protocol ends towards the UE 11. The ng-eNB 22 provides E-UTRA user plane and control plane protocol ends towards the UE 11.
The 5GC includes an access and mobility management function (AMF), a User Plane Function (UPF), and a Session Management Function (SMF). The AMF hosts functions such as NAS security, idle state mobility handling, etc. The AMF is an entity including the functionality of a conventional MME. UPF hosts functions such as mobility anchoring, protocol Data Unit (PDU) processing. UPF is an entity that includes the functionality of a legacy S-GW. SMF hosts functions such as UE IP address allocation, PDU session control.
The gNB and the ng-eNB are interconnected to each other by an Xn interface. The gNB and NG-eNB are also connected to the 5GC via a NG interface, more specifically to the AMF via a NG-C interface and to the UPF via a NG-U interface.
Protocol structures between the above-described network entities are described. On the systems of fig. 1 and/or fig. 2, layers of a radio interface protocol between a UE and a network (e.g., NG-RAN and/or E-UTRAN) may be classified into a first layer (L1), a second layer (L2), and a third layer (L3) based on the lower three layers of an Open System Interconnection (OSI) model well known in communication systems.
Fig. 3 shows a block diagram of a user plane protocol stack to which the technical features of the present invention may be applied. Fig. 4 shows a block diagram of a control plane protocol stack to which the technical features of the present invention may be applied. The user/control plane protocol stacks shown in fig. 3 and 4 are used in NR. However, without loss of generality, the user/control plane protocol stacks shown in fig. 3 and 4 may be used in LTE/LTE-a by replacing the gNB/AMF with an eNB/MME.
Referring to fig. 3 and 4, a Physical (PHY) layer belongs to L1. The PHY layer provides information transfer services to a Medium Access Control (MAC) sub-layer and higher layers. The PHY layer provides transport channels to the MAC sublayer. Data between the MAC sublayer and the PHY layer is transferred via a transport channel. Data is transferred between different PHY layers (i.e., between a PHY layer of a sender and a PHY layer of a receiver) via a physical channel.
The MAC sublayer belongs to L2. The main services and functions of the MAC sublayer include mapping between logical channels and transport channels, multiplexing of MAC Service Data Units (SDUs) belonging to one or different logical channels into/from Transport Blocks (TBs) transmitted to/from the physical layer on the transport channels, scheduling information reporting, error correction by hybrid automatic repeat request (HARQ), priority handling between UEs by dynamic scheduling, priority handling between logical channels of one UE by logical channel priority order (LCP), etc. The MAC sublayer provides logical channels to the Radio Link Control (RLC) sublayer.
The RLC sublayer belongs to L2. The RLC sublayer supports three transmission modes, namely, a Transparent Mode (TM), an Unacknowledged Mode (UM), and an Acknowledged Mode (AM), in order to guarantee various quality of service (QoS) required for a radio bearer. The main services and functions of the RLC sublayer depend on the transmission mode. For example, the RLC sublayer provides transmission of upper layer PDUs for all three modes, but provides error correction by ARQ only for AM. In LTE/LTE-a, the RLC sublayer provides concatenation, segmentation and reassembly of RLC SDUs (for UM and AM data transfer only) and re-segmentation of RLC data PDUs (for AM data transfer only). In NR, the RLC sublayer provides segmentation (for AM and UM only) and re-segmentation (for AM only) of RLC SDUs and reassembly (for AM and UM only) of SDUs. That is, NR does not support concatenation of RLC SDUs. The RLC sublayer provides RLC channels to a Packet Data Convergence Protocol (PDCP) sublayer.
The PDCP sublayer belongs to L2. The main services and functions of the PDCP sublayer for the user plane include header compression and decompression, transfer of user data, duplicate detection, PDCP PDU routing, retransmission of PDCP SDUs, ciphering and deciphering, and the like. The main services and functions of the PDCP sublayer for the control plane include ciphering and integrity protection, transfer of control plane data, and the like.
The Service Data Adaptation Protocol (SDAP) sublayer belongs to L2. The SDAP sub-layer is defined only in the user plane. The SDAP sub-layer is defined only for NR. The main services and functions of the SDAP include mapping between QoS flows and Data Radio Bearers (DRBs) and marking QoS Flow IDs (QFIs) in both DL and UL packets. The SDAP sublayer provides QoS flows to the 5 GC.
The Radio Resource Control (RRC) layer belongs to L3. The RRC layer is defined only in the control plane. The RRC layer controls radio resources between the UE and the network. For this, the RRC layer exchanges RRC messages between the UE and the BS. The main services and functions of the RRC layer include broadcasting system information related to the AS and NAS, paging, establishment, maintenance and release of RRC connection between UE and network, security functions including key management, establishment, configuration, maintenance and release of radio bearers, mobility functions, qoS management functions, UE measurement reports and control of reports, NAS messaging from UE to NAS/from NAS to UE.
In other words, the RRC layer controls logical channels, transport channels, and physical channels with respect to configuration, reconfiguration, and release of radio bearers. The radio bearer refers to a logical path provided by L1 (PHY layer) and L2 (MAC/RLC/PDCP/SDAP sub-layer) for data transmission between the UE and the network. Setting a radio bearer means defining characteristics of a radio protocol layer and a channel providing a specific service, and setting respective specific parameters and operation methods. The radio bearers may be divided into Signaling RBs (SRBs) and Data RBs (DRBs). The SRB serves as a path for transmitting RRC messages in the control plane, and the DRB serves as a path for transmitting user data in the user plane.
The RRC state indicates whether the RRC layer of the UE is logically connected to the RRC layer of the E-UTRAN. In LTE/LTE-a, the UE is in an RRC CONNECTED state (rrc_connected) when an RRC connection is established between the RRC layer of the UE and the RRC layer of the E-UTRAN. Otherwise, the UE is in an RRC IDLE state (rrc_idle). In NR, an RRC INACTIVE state (rrc_inactive) is additionally introduced. Rrc_inactive may be used for various purposes. For example, a large-scale machine type communication (MMTC) UE may be effectively managed under rrc_inactive. When a specific condition is satisfied, a transition is made from one of the three states to the other.
The predetermined operation may be performed according to the RRC state. Under rrc_idle, public Land Mobile Network (PLMN) selection, broadcasting of System Information (SI), cell reselection mobility, core Network (CN) paging, and Discontinuous Reception (DRX) configured by NAS may be performed. The UE should have been assigned an Identifier (ID) that uniquely identifies the UE in the tracking area. The RRC context is not stored in the base station.
In rrc_connected, the UE has an RRC connection with the network (i.e., E-UTRAN/NG-RAN). A network-CN connection (both C-plane/U-plane) is also established for the UE. UE AS context is stored in the network and UE. The RAN knows the cell to which the UE belongs. The network may send data to and/or receive data from the UE. Network control mobility including measurements is also performed.
Most of the operations performed under rrc_idle may be performed under rrc_inactive. However, instead of CN paging under rrc_idle, RAN paging is performed under rrc_inactive. In other words, under rrc_idle, paging of Mobile Termination (MT) data is initiated by the core network, and the paging area is managed by the core network. Under rrc_inactive paging is initiated by NG-RA and the RAN-based notification area (RNA) is managed by NG-RAN. Furthermore, instead of DRX for CN paging configured by NAS under rrc_idle, DRX for RAN paging is configured by NG-RAN under rrc_inactive. Further, under rrc_inactive, a 5GC-NG-RAN connection (both C-plane/U-plane) is established for the UE, and the UE AS context is stored in NG-RAN and UE. The NG-RAN knows the RNA to which the UE belongs.
The NAS layer is located on top of the RRC layer. The NAS control protocol performs functions such as authentication, mobility management, security control.
The physical channel may be modulated according to the OFDM process and utilize time and frequency as radio resources. The physical channel is composed of a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols in the time domain and a plurality of subcarriers in the frequency domain. One subframe is composed of a plurality of OFDM symbols in the time domain. A resource block is a resource allocation unit and is composed of a plurality of OFDM symbols and a plurality of subcarriers. In addition, each subframe may use a specific subcarrier of a specific OFDM symbol (e.g., a first OFDM symbol) of a corresponding subframe for a Physical Downlink Control Channel (PDCCH), i.e., an L1/L2 control channel. A Transmission Time Interval (TTI) is a basic unit of time for a scheduler to allocate resources. The TTI may be defined in units of one or more slots or may be defined in units of mini slots.
The transmission channels are classified according to how and with what characteristics data is transmitted via the radio interface. The DL transport channels include a Broadcast Channel (BCH) for transmitting system information, a downlink shared channel (DL-SCH) for transmitting user traffic or control signals, and a Paging Channel (PCH) for paging the UE. The UL transport channel includes an uplink shared channel (UL-SCH) for transmitting user traffic or control signals and a Random Access Channel (RACH) generally used for an initial access cell.
The MAC sublayer provides different types of data transfer services. Each logical channel type is defined by what type of information is transmitted. Logical channels are classified into two groups: control channels and traffic channels.
The control channel is used only to transmit control plane information. Control channels include Broadcast Control Channel (BCCH), paging Control Channel (PCCH), common Control Channel (CCCH), and Dedicated Control Channel (DCCH). The BCCH is a DL channel for broadcasting system control information. The PCCH is a DL channel that transmits paging information, a system information change notification. The CCCH is a channel for transmitting control information between the UE and the network. The channel is for UEs that have no RRC connection with the network. DCCH is a point-to-point bi-directional channel that transmits dedicated control information between a UE and a network. The channel is used by UEs with RRC connections.
The traffic channel is used only to transmit user plane information. The traffic channels include Dedicated Traffic Channels (DTCH). DTCH is a point-to-point channel dedicated to one UE transmitting user information. DTCH may be present in both UL and DL.
Regarding mapping between logical channels and transport channels, in DL, a BCCH may be mapped to a BCH, a BCCH may be mapped to a DL-SCH, a PCCH may be mapped to a PCH, a CCCH may be mapped to a DL-SCH, a DCCH may be mapped to a DL-SCH, and a DTCH may be mapped to a DL-SCH. In the UL, the CCCH may be mapped to the UL-SCH, the DCCH may be mapped to the UL-SCH, and the DTCH may be mapped to the UL-SCH.
Rrc_inactive is the state where the UE remains in CM-CONNECTED and can move within the NG-RAN (RNA) configured area without informing the NG-RAN. Under rrc_inactive, the last serving gNB node maintains the UE context and NG connections associated with UEs serving AMF and UPF.
If the last serving gNB receives DL data from the UPF or DL signaling from the AMF while the UE is in rrc_inactive, it pages in the cell corresponding to the RNA, and if the RNA includes cells of neighboring gnbs, an XnAP RAN page may be sent to the neighboring gNB.
A UE in rrc_inactive state may be configured with RNA, wherein:
The RNA may cover a single or multiple cells and may be smaller than the CN area;
-a RAN-based notification area update (RNAU) is sent periodically by the UE and also sent when the cell reselection procedure of the UE selects a cell not belonging to the configured RNA.
There are a number of different options as to how RNA can be configured:
list of cells:
-providing the UE with an explicit list of cell(s) constituting RNA.
List of RAN areas:
-providing the UE with (at least one) RAN area ID, wherein the RAN area is a subset of the CN tracking area;
the cell broadcasts the (at least one) RAN area ID in the system information so that the UE knows which area the cell belongs to.
The UE triggers the transition from rrc_inactive to rrc_connected as follows.
Fig. 5 illustrates an RRC connection recovery procedure.
In step S502, the UE is in an rrc_inactive/CM connected state.
In step S504, the UE recovers from rrc_inactive and provides the I-RNTI and appropriate cause values (e.g., RAN notification area update) allocated by the previous serving gNB.
In step S506, if the gNB identity contained in the I-RNTI can be resolved, the gNB requests the previous serving gNB to provide the UE context.
In step S508, the previous serving gNB provides the UE context.
In step S510, the gNB may move the UE to rrc_connected, or send the UE back to rrc_inactive state or send the UE to rrc_idle. If the UE is transmitted to rrc_idle, the following steps are not required.
In step S512, the gNB provides a forwarding address if the loss of DL user data buffered in the previous serving gNB should be prevented.
In steps S514 and S516, the gNB performs path switching.
In step S518, the gNB triggers release of UE resources at the last serving gNB.
After step S502 described above, SRB0 (no security) may be used when the gNB decides to reject the resume request and keep the UE at rrc_inactive without any reconfiguration, or when the gNB decides to establish a new RRC connection. SRB1 (with at least integrity protection) should be used when the gNB decides to reconfigure the UE (e.g., with a new DRX cycle or RNA) or when the gNB decides to push the UE towards rrc_idle.
As described above, the periodic RNAU may be performed using an RRC connection recovery procedure. However, referring to fig. 5, context acquisition may occur whenever the UE transitions from the RRC-INACTIVE state to the RRC-CONNECTED state to perform RNAU. In particular, whenever a UE accesses the gNB to inform the network that it is still reachable in the RAN-based notification area, the UE context should be acquired from the previous serving gNB to the new gNB. However, since no data transmission between the UE and the gNB may occur during the RNAU, transmitting the UE context towards the new gNB results in unnecessary signaling and additional delay. Thus, the anchor gNB needs to skip the UE context acquisition procedure towards the new gNB during the periodic RNAU.
Hereinafter, a method of managing a UE context according to an embodiment of the present invention is described. In this embodiment, the problem of efficient UE context management during periodic RAN-based notification area updates (RNAUs) is addressed.
Fig. 6 illustrates an example of a method of managing UE context according to an embodiment of the present invention. In this embodiment, it may be suggested that when data transmission is not needed and when the reachability of the UE is confirmed by the periodic RNAU, the anchor gNB may determine to maintain the role of the anchor gNB and may skip UE context transfer towards the new gNB. In other words, the anchor gNB may not perform unnecessary UE context acquisition. In order for the new gNB to move the UE back to the RRC-INACTIVE state with at least integrity protection, the anchor gNB may generate an RRC message based on the SRB1 configuration of the new gNB to keep the UE in the rrc_inactive state.
In this embodiment, the anchor gNB may be a base station of a cell in which the UE was previously located, and the new gNB may be a base station of a cell in which the UE is currently located. In other words, the UE was served by the anchor gNB, and the UE transitioned to RRC inactivity while being served by the anchor gNB. Thereafter, while the UE is in the RRC inactive state, the UE moves toward another gNB (e.g., a new gNB). Further, it is assumed that the anchor gNB and the new gNB are in the same RAN-based notification area. Hereinafter, the anchor gNB may be a previous service gNB (may also be referred to as gNB 1). The new gNB may be a current serving gNB (also may be referred to as gNB 2).
In step S602, the UE may be in an RRC-INACTIVE state. The NG connection between the gNB1 and NGC is maintained.
In step S604, when the reachability timer (i.e., the periodic RNAU timer) in the UE expires, the UE may trigger a periodic RNAU procedure to notify the network that the UE is still reachable in the RAN-based notification area. When the UE moves to the gNB2 other than the anchor gNB (=gnb1), the UE can access the gNB2 since the gNB1 and the gNB2 are in the same RAN-based notification area. Thus, a UE in RRC-INACTIVE state may send a message for accessing the gNB. For example, the UE may send a random access preamble message, an RRC resume request message, or a new message to the gNB2.
In step S606, the gNB2 may respond to the UE upon receiving a message from the UE. For example, the gNB2 may send a random access response message to the UE.
In step S608, to restore the RRC connection, the UE may send an RRC restoration request message or a new message to the gNB2. This message may include a resume ID to identify the UE context in the gNB. The RRC establishment cause for the RNAU is included in this message to inform the network to trigger the RNAU. In other words, the UE may send a message informing RRC connection recovery related to the RNAU. For example, the UE may provide the I-RNTI and appropriate cause values (e.g., RAN notification area update) allocated by the previous serving gNB.
In step S610, upon receiving the RRC resume request message or the new message, the gNB2 may check whether the UE context related to the resume ID can be found. If not, gNB2 may identify an anchor gNB (=gnb1) with an Xn interface providing the resume ID. When the anchor gNB (=gnb1) is found, gNB2 may decide to acquire the UE context from gNB1 using the existing retrieve UE context procedure or the new procedure via the Xn interface. Thus, the gNB2 may send a UE context request message or a new message to the gNB 1. The UE context request message may be a retrieve UE context request message. The message may include a location update indication or an RRC establishment cause to indicate that the UE accesses the gNB2 in order to check reachability. In addition, the SRB1 configuration of the gNB2 may be included in the message. That is, if the gNB identity contained in the I-RNTI can be parsed, the gNB2 may request that the previous serving gNB provide the UE context, thereby providing the cause value received in step S610.
In step S612, upon receiving a message including the resume ID from the UE, the gNB1 may check whether it can find the UE context related to the resume ID. Based on retrieving the RRC establishment cause or location update indication in the UE context request message, the gNB1 may also know that the procedure is an RNAU that the UE informs the network that it is still reachable. When the UE context is found accurately based on the recovery ID, gNB1 may reset the RNAU timer for that UE. Then, if the UE remains within the same RAN-based notification area and there is no data transmission between the gNB1 and the UE, the gNB1 may decide to keep the role of the anchor gNB. In this case, gNB1 may not forward the UE context to gNB2. In order for the gNB2 to move the UE back to the RRC-INACTIVE state with at least integrity protection, the gNB1 may generate an RRC message that keeps the UE in the RRC_INACTIVE state. The RRC message may request the UE to move to the rrc_inactive state. For example, the RRC message may be an RRC release message.
In step S614, the gNB1 may send an RRC message to the gNB2 via the container in the UE context response message. That is, the UE context response message may include a container of piggybacked RRC messages. The UE context response message may be a retrieve UE context failure message including an encapsulated RRC release message. Further, if the last serving gNB decided to keep the UE at rrc_inactive, the RRC release message may include a suspension configuration. If the RRC release message does not include a suspension configuration, the UE that received the RRC release message may transition to the rrc_idle state. The UE context response message may not include the UE context.
In step S616, upon receiving the message from gNB1, gNB2 may know the intent of the anchor gNB: it decides not to reassign the anchor gNB. Thus, the gNB2 may not trigger a path switching procedure towards the NGC. The gNB2 may transparently forward RRC messages to the UE. Thus, the gNB2 may forward the RRC release message and suspension configuration to the UE. The RRC message sent by the gNB2 to the UE may be at least one of an RRC resume message or an RRC release message.
In step S618, the UE may still be in the RRC-INACTIVE state.
According to embodiments of the present invention, when the periodic RNAU is triggered, the anchor gNB may remove unnecessary signaling by skipping UE context acquisition towards the new gNB.
Fig. 7 illustrates another example of a method of managing UE context according to an embodiment. In this embodiment, it may be suggested that the anchor gNB may determine to maintain the role of the anchor gNB when no data transmission is required and the reachability of the UE is confirmed by the periodic RNAU. However, in order for the new gNB to move the UE back to the RRC-INACTIVE state with at least integrity protection, the anchor gNB may transmit a UE context and context release indication to the new gNB. Based on the indication, the new gNB may allow its context to be released for the UE after generating and sending an RRC resume message or an RRC release message to the UE.
In this embodiment, the anchor gNB may be a base station of a cell in which the UE was previously located, and the new gNB may be a base station of a cell in which the UE is currently located. In other words, the UE was served by the anchor gNB, and the UE transitioned to RRC inactivity while being served by the anchor gNB. Thereafter, while the UE is in the RRC inactive state, the UE moves toward another gNB (e.g., a new gNB). Further, it is assumed that the anchor gNB and the new gNB are in the same RAN-based notification area. Hereinafter, the anchor gNB may be a previous service gNB (may also be referred to as gNB 1). The new gNB may be a current serving gNB (also may be referred to as gNB 2).
In step S702, the UE may be in an RRC-INACTIVE state. The NG connection between the gNB1 and NGC is maintained.
In step S704, when the reachability timer in the UE expires, the UE may trigger a periodic RNAU procedure to notify the network that the UE is still reachable in the RAN-based notification area. When the UE moves to the gNB2 other than the anchor gNB (=gnb1), the UE can access the gNB2 since the gNB1 and the gNB2 are in the same RAN-based notification area. Thus, a UE in RRC-INACTIVE state may send a message for accessing the gNB. For example, the UE may send a random access preamble message, an RRC resume request message, or a new message to the gNB2.
In step S706, the gNB2 may respond to the UE upon receiving the message from the UE. For example, the gNB2 may send a random access response message to the UE.
In step S708, to restore the RRC connection, the UE may send an RRC restoration request message or a new message to the gNB2. The message may include a resume ID to identify the UE context in the gNB. The message includes the RRC establishment cause for the RNAU to inform the network to trigger the RNAU. In other words, the UE may send a message informing RRC connection recovery related to the RNAU. For example, the UE may provide the I-RNTI and appropriate cause values (e.g., RAN notification area update) allocated by the previous serving gNB.
In step S710, upon receiving the RRC resume request message or the new message, the gNB2 may check whether the UE context related to the resume ID can be found. If not, gNB2 may identify an anchor gNB (=gnb1) with an Xn interface providing the resume ID. When the anchor gNB (=gnb1) is found, gNB2 may decide to acquire the UE context from gNB1 using the existing retrieve UE context procedure or the new procedure via the Xn interface. Thus, the gNB2 may send a UE context request message or a new message to the gNB 1. The UE context request message may be a retrieve UE context request message. The message may include a location update indication or an RRC establishment cause to indicate that the UE accesses the gNB2 in order to check reachability. That is, if the gNB identity contained in the I-RNTI can be resolved, the gNB2 may request that the last serving gNB provide the UE context, thereby providing the cause value received in step S708 (via the RRC resume request message).
In step S712, upon receiving a message including the resume ID from the UE, the gNB1 may check whether it can find the UE context related to the resume ID. Based on retrieving the RRC establishment cause or location update indication in the UE context request message, the gNB1 may also know that the procedure is an RNAU that the UE informs the network that it is still reachable. When the UE context is found accurately based on the recovery ID, gNB1 may reset the RNAU timer for that UE. Then, if the UE remains within the same RAN-based notification area and there is no data transmission between the gNB1 and the UE, the gNB1 may decide to keep the role of the anchor gNB.
In step S714, the gNB1 may send a UE context response message or a new message to the gNB 2. The UE context response may be a retrieve UE context response message. The context release indication may also be included with the UE context response message when the gNB1 decides not to reallocate the anchor gNB.
In step S716, upon receiving the message from gNB1, gNB2 may know the intent of the anchor gNB based on the context release indication: it decides not to reassign the anchor gNB. Thus, the gNB2 generates and sends an RRC connection resume message to the UE based only on the UE context received from gNB1 to move the UE back to the RRC-INACTIVE state with at least integrity protection.
In step S718, the UE may still be in the RRC-INACTIVE state.
In step S720, the gNB2 may release the context of the UE in the RRC-INACTIVE state.
According to embodiments of the present invention, when the periodic RNAU is triggered, the anchor gNB may remove unnecessary signaling by skipping UE context acquisition towards the new gNB.
Furthermore, embodiments of the present invention are also applicable to CU-DU splitting in the NR case where the UE context is restored in RRC-INACTIVE UE. This solution may also be applied to CU-DU splitting in the LTE case of restoring UE context in NB-IoT UEs and lightly connected UEs.
According to embodiments of the present invention, if the UE transmits a periodic RNAU and does not need to move the UE's context to the serving gNB, the previous serving gNB does not need to transmit the UE context to the current serving gNB, and the current serving gNB does not need to perform the core network and path switching procedure. That is, the anchor gNB may selectively acquire UE context toward the new gNB in order to reassign the role of the anchor gNB. For periodic RNAU, the anchor gNB may decide whether to transmit the UE context to the new gNB as the UE moves back to the RRC-INACTIVE state. In addition, the anchor gNB may confirm the reachability of the UE without a state transition procedure. Thus, these embodiments may make the UE experience better (e.g., state transitions from RRC-INACTIVE state (or light connection in LTE) to RRC-CONNECTED state may be removed).
Fig. 8 illustrates an example of a method of managing UE context according to the present invention.
In step S802, a first Base Station (BS) may receive a UE context request message including a Radio Resource Control (RRC) establishment cause from a second BS. The first BS and the second BS may be located in the same Radio Access Network (RAN) -based notification area (RNA). The first BS may be a previous serving base station and the second BS may be a current serving base station.
In step S804, when the RRC establishment cause relates to RNA update, the first base station may transmit a UE context response message to the second BS. The UE context response message may piggyback an RRC message requesting the UE to move to an RRC inactive state. The first base station may determine that the first BS maintains the UE context based on RRC establishment cause related to RNA update. Further, the first base station may generate a UE context response message that does not include the UE context requested by the UE context request message. The RRC message may be an RRC resume message or an RRC release message. The UE context response message may be a retrieve UE context failure message.
According to embodiments of the present invention, if the UE transmits a periodic RNAU and does not need to move the UE's context to the serving gNB, the previous serving gNB does not need to transmit the UE context to the current serving gNB, and the current serving gNB does not need to perform the core network and path switching procedure. That is, the anchor gNB may selectively acquire UE context toward the new gNB in order to reassign the role of the anchor gNB. For periodic RNAU, the anchor gNB may decide whether to transmit the UE context to the new gNB as the UE moves back to the RRC-INACTIVE state.
Fig. 9 shows a structure of a network according to an embodiment of the present invention. The first network node 910 shown in fig. 9 may be a first Base Station (BS), which may be one of an eNB or a gNB. The second network node 920 may be a second BS, which may be one of an eNB or a gNB.
The first network node 910 comprises a processor 911, a memory 912 and a transceiver 913. The memory 912 is coupled to the processor 911 and stores various information for driving the processor 911. The transceiver 913 is coupled to the processor 911 and transmits and/or receives radio signals. The processor 911 implements the proposed functions, procedures and/or methods. In the above-described embodiments, the operations of the first network node may be implemented by the processor 911.
The processor 911 may include an Application Specific Integrated Circuit (ASIC), other chipset, logic circuit, and/or data processing device. The memory may include Read Only Memory (ROM), random Access Memory (RAM), flash memory, memory cards, storage media, and/or other storage devices. The transceiver may include baseband circuitry to process radio frequency signals. When the embodiments are implemented in software, the techniques described herein may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules may be stored in memory and executed by a processor. The memory may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.
The processor 911 may be configured to control the transceiver 913 to receive a UE context request message including a Radio Resource Control (RRC) establishment cause from the second BS. The first BS and the second BS may be located in the same Radio Access Network (RAN) -based notification area (RNA). The first BS may be a previous serving base station and the second BS may be a current serving base station.
If the RRC establishment cause relates to the RNA update, the processor 911 may be configured to control the transceiver 913 to transmit a UE context response message to the second BS. The UE context response message may piggyback an RRC message requesting the UE to move to an RRC inactive state. The first base station may determine that the first BS maintains the UE context based on RRC establishment cause related to RNA update. Further, the first base station may generate a UE context response message that does not include the UE context requested by the UE context request message. The RRC message may be an RRC resume message or an RRC release message. The UE context response message may be a retrieve UE context failure message.
According to embodiments of the present invention, if the UE transmits a periodic RNAU and does not need to move the UE's context to the serving gNB, the previous serving gNB does not need to transmit the UE context to the current serving gNB, and the current serving gNB does not need to perform the core network and path switching procedure. That is, the anchor gNB may selectively acquire UE context toward the new gNB in order to reassign the role of the anchor gNB. For periodic RNAU, the anchor gNB may decide whether to transmit the UE context to the new gNB as the UE moves back to the RRC-INACTIVE state.
Fig. 10 illustrates an example of a method of managing UE context according to the present invention.
In step S1002, the second Base Station (BS) may receive an RRC resume request message including an RRC establishment cause from the User Equipment (UE). The RRC establishment cause may relate to a Radio Access Network (RAN) based notification area (RNA) update. The first BS may be a previous serving base station and the second BS may be a current serving base station.
In step S1004, the second BS may transmit a UE context request message including an RRC establishment cause to the first BS. The first BS and the second BS may be located in the same RNA.
In step S1006, the second BS may receive a UE context response message from the first BS. The UE context response message may piggyback an RRC message requesting the UE to move to an RRC inactive state. The UE context response message may not include the UE context requested by the UE context request message. The UE context response message may be a retrieve UE context failure message.
In step S1008, the second BS may forward the RRC message to the UE.
According to embodiments of the present invention, if the UE transmits a periodic RNAU and does not need to move the UE's context to the serving gNB, the previous serving gNB does not need to transmit the UE context to the current serving gNB, and the current serving gNB does not need to perform the core network and path switching procedure. That is, the anchor gNB may selectively acquire UE context toward the new gNB in order to reassign the role of the anchor gNB. For periodic RNAU, the anchor gNB may decide whether to transmit the UE context to the new gNB as the UE moves back to the RRC-INACTIVE state.
Fig. 11 shows a structure of a network according to an embodiment of the present invention. The first network node 1110 shown in fig. 11 may be a first Base Station (BS), which may be one of an eNB or a gNB. The second network node 1120 may be a second BS and the second network node 1120 may be a UE.
The second network node 1120 includes a processor 1121, a memory 1122, and a transceiver 1123. The memory 1122 is coupled to the processor 1121 and stores various information for driving the processor 1121. The transceiver 1123 is coupled to the processor 1121 and transmits and/or receives radio signals. The processor 1121 implements the proposed functions, procedures and/or methods. In the above embodiments, the operation of the first network node may be implemented by the processor 1121.
Processor 1121 may include an Application Specific Integrated Circuit (ASIC), other chipset, logic circuit, and/or data processing device. The memory may include Read Only Memory (ROM), random Access Memory (RAM), flash memory, memory cards, storage media, and/or other storage devices. The transceiver may include baseband circuitry to process radio frequency signals. When the embodiments are implemented in software, the techniques described herein may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules may be stored in memory and executed by a processor. The memory may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.
The processor 1121 may be configured to control the transceiver 1123 to receive an RRC resume request message including an RRC establishment cause from a User Equipment (UE). The RRC establishment cause may relate to a Radio Access Network (RAN) based notification area (RNA) update. The first BS may be a previous serving base station and the second BS may be a current serving base station.
The processor 1121 may be configured to control the transceiver 1123 to transmit a UE context request message including an RRC establishment cause to the first BS. The first BS and the second BS may be located in the same RNA.
The processor 1121 may be configured to control the transceiver 1123 to receive a UE context response message from the first BS. The UE context response message may piggyback an RRC message requesting the UE to move to an RRC inactive state. The UE context response message may not include the UE context requested by the UE context request message. The UE context response message may be a retrieve UE context failure message.
The processor 1121 may be configured to control the transceiver 1123 to forward an RRC message requesting the UE to move to an RRC inactive state.
According to embodiments of the present invention, if the UE transmits a periodic RNAU and does not need to move the UE's context to the serving gNB, the previous serving gNB does not need to transmit the UE context to the current serving gNB, and the current serving gNB does not need to perform the core network and path switching procedure. That is, the anchor gNB may selectively acquire UE context toward the new gNB in order to reassign the role of the anchor gNB. For periodic RNAU, the anchor gNB may decide whether to transmit the UE context to the new gNB as the UE moves back to the RRC-INACTIVE state.
Fig. 12 illustrates an example of a method of managing UE context according to the present invention.
In step S1202, the UE may transmit an RRC resume request message including an RRC establishment cause from a User Equipment (UE) to the second BS. The RRC establishment cause may relate to a Radio Access Network (RAN) based notification area (RNA) update. The second BS may be the current serving base station.
In step S1204, the UE may receive an RRC message from the second BS requesting the UE to move to an RRC inactive state.
According to embodiments of the present invention, if the UE transmits a periodic RNAU and does not need to move the UE's context to the serving gNB, the previous serving gNB does not need to transmit the UE context to the current serving gNB, and the current serving gNB does not need to perform the core network and path switching procedure. That is, the anchor gNB may selectively acquire UE context toward the new gNB in order to reassign the role of the anchor gNB. For periodic RNAU, the anchor gNB may decide whether to transmit the UE context to the new gNB as the UE moves back to the RRC-INACTIVE state.
Fig. 13 illustrates a structure of a UE according to an embodiment of the present invention.
According to an embodiment of the present invention, the UE 1300 may include a transceiver 1301, a processor 1302, and a memory 1303. A memory 1303 is coupled to the processor 1302 and stores various information for driving the processor 1302. The transceiver 1301 is coupled to the processor 1302 and transmits and/or receives radio signals. The processor 1302 implements the proposed functions, procedures and/or methods. In the above embodiments, the operations of the UE 1300 may be implemented by the processor 1302.
The processor 1302 can include Application Specific Integrated Circuits (ASICs), other chipsets, logic circuits, and/or data processing devices. Memory 1303 may include read-only memory (ROM), random-access memory (RAM), flash memory, memory cards, storage media, and/or other storage devices. The transceiver 1301 may include baseband circuitry to process radio frequency signals. When the embodiments are implemented in software, the techniques described herein may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules may be stored in memory and executed by the processor 1302. The memory 1303 may be implemented within the processor 1302 or external to the processor 1302, in which case the memory can be communicatively coupled to the processor 1302 via various means as is known in the art.
The processor 1302 may be configured to control the transceiver 1301 to transmit an RRC recovery request message including an RRC establishment cause from a User Equipment (UE) to the second BS. The RRC establishment cause may relate to a Radio Access Network (RAN) based notification area (RNA) update. The second BS may be the current serving base station.
The processor 1302 may be configured to control the transceiver 1301 to receive an RRC message from the second BS requesting the UE to move to the RRC inactive state.
According to embodiments of the present invention, if the UE transmits a periodic RNAU and does not need to move the UE's context to the serving gNB, the previous serving gNB does not need to transmit the UE context to the current serving gNB, and the current serving gNB does not need to perform the core network and path switching procedure. That is, the anchor gNB may selectively acquire UE context toward the new gNB in order to reassign the role of the anchor gNB. For periodic RNAU, the anchor gNB may decide whether to transmit the UE context to the new gNB as the UE moves back to the RRC-INACTIVE state.
In view of the exemplary systems described herein, methodologies that may be implemented in accordance with the disclosed subject matter are described with reference to a number of flowcharts. While, for purposes of simplicity, the methodologies are shown and described as a series of steps or blocks, it is to be understood and appreciated that the claimed subject matter is not limited by the order of the steps or blocks, as some steps may occur in different orders or concurrently with other steps from that depicted and described herein. Moreover, those of skill in the art will understand that the steps shown in the flowcharts are not exclusive and that other steps may be included or one or more steps in the example flowcharts may be deleted without affecting the scope and spirit of the present disclosure.
The foregoing includes examples of aspects. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the various aspects, but one of ordinary skill in the art may recognize that many further combinations and permutations are possible. Accordingly, the present specification is intended to embrace all such alterations, modifications and variations that fall within the scope of the appended claims.

Claims (6)

1. A method performed by a first base station BS in a wireless communication system, the method comprising the steps of:
receiving from a second BS a retrieve UE context request message comprising (1) a cause of a radio access network RAN based notification area RNA update informing a user equipment UE and (2) a signaling radio bearer SRB configuration associated with said second BS,
wherein the reason informing of the RNA update is sent from the UE via a radio resource control, RRC, connection resume request message;
deciding to skip transmission of UE context for the UE based on the reason informing of the RNA update;
generating an RRC connection resume message based on the SRB configuration associated with the second BS; and
transmitting a response message to the second BS in response to the retrieve UE context request message, wherein the response message includes a container piggybacking the RRC connection resume message for requesting the UE to move to an RRC inactive state,
Wherein the RRC connection restoration message is transparently forwarded to the UE via the second BS, and
wherein the first BS and the second BS are located in the same RNA.
2. The method of claim 1, wherein the response message does not include the UE context.
3. The method of claim 1, wherein the first BS is a previous serving base station and the second BS is a current serving base station.
4. A first base station, BS, in a wireless communication system, the first BS comprising:
a transceiver; and
a processor coupled to the transceiver,
wherein the first BS is configured to:
receiving from a second BS a retrieve UE context request message comprising (1) a cause of a radio access network RAN based notification area RNA update informing a user equipment UE and (2) a signaling radio bearer SRB configuration associated with said second BS,
wherein the reason informing of the RNA update is sent from the UE via a radio resource control, RRC, connection resume request message;
deciding to skip transmission of UE context for the UE based on the reason informing of the RNA update;
generating an RRC connection resume message based on the SRB configuration associated with the second BS; and is also provided with
Transmitting a response message to the second BS in response to the retrieve UE context request message, wherein the response message includes a container piggybacking the RRC connection resume message for requesting the UE to move to an RRC inactive state,
wherein the RRC connection restoration message is transparently forwarded to the UE via the second BS, and
wherein the first BS and the second BS are located in the same RNA.
5. The first BS of claim 4, wherein the response message does not include the UE context.
6. The first BS of claim 4, wherein the first BS is a previous serving base station and the second BS is a current serving base station.
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